A well-known ski boot, of the type involving entry of the foot from the rear, such as that described, for example, in U.S. Pat. No. 4,677,770, incorporates elastic means for controlling the flexion of the shaft; these means are found in the area of the pin which joints the rear cover to the rear extension components of the sleeve. In order to allow a ski boot of this type to be put on and removed by means of a rearward pivoting of the rear cover around the jointing pin which connects the cover to the rear extension components of the sleeve, the elastic means for controlling flexion are arranged in such a way as to cause interaction between said jointing pin and the shell base. This arrangement gives freedom of rotation to the jointing pin; however, because of the relative proximity of this pin to the shell base, and especially to its stopping system, the design and lay-out of the elastic means of flexion control must be delicately determined in the space left free in the posterior region of the boot. Furthermore, because of the action exerted directly by the elastic means on the jointing pin, the pivoting of this pin is somewhat hindered, at least for the value ascribed to friction.